package com.admin.common.utils.html;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * HTML过滤器，用于去除XSS漏洞隐患。
 *
 * @author fangchen
 */
public final class HTMLFilter {
    /**
     * regex flag union representing /si modifiers in php
     **/
    private static final int REGEX_FLAGS_SI = Pattern.CASE_INSENSITIVE | Pattern.DOTALL;
    private static final Pattern P_COMMENTS = Pattern.compile( "<!--(.*?)-->", Pattern.DOTALL );
    private static final Pattern P_COMMENT = Pattern.compile( "^!--(.*)--$", REGEX_FLAGS_SI );
    private static final Pattern P_TAGS = Pattern.compile( "<(.*?)>", Pattern.DOTALL );
    private static final Pattern P_END_TAG = Pattern.compile( "^/([a-z0-9]+)", REGEX_FLAGS_SI );
    private static final Pattern P_START_TAG = Pattern.compile( "^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI );
    private static final Pattern P_QUOTED_ATTRIBUTES = Pattern.compile( "([a-z0-9]+)=([\"'])(.*?)\\2", REGEX_FLAGS_SI );
    private static final Pattern P_UNQUOTED_ATTRIBUTES = Pattern.compile( "([a-z0-9]+)(=)([^\"\\s']+)", REGEX_FLAGS_SI );
    private static final Pattern P_PROTOCOL = Pattern.compile( "^([^:]+):", REGEX_FLAGS_SI );
    private static final Pattern P_ENTITY = Pattern.compile( "&#(\\d+);?" );
    private static final Pattern P_ENTITY_UNICODE = Pattern.compile( "&#x([0-9a-f]+);?" );
    private static final Pattern P_ENCODE = Pattern.compile( "%([0-9a-f]{2});?" );
    private static final Pattern P_VALID_ENTITIES = Pattern.compile( "&([^&;]*)(?=(;|&|$))" );
    private static final Pattern P_VALID_QUOTES = Pattern.compile( "(>|^)([^<]+?)(<|$)", Pattern.DOTALL );
    private static final Pattern P_END_ARROW = Pattern.compile( "^>" );
    private static final Pattern P_BODY_TO_END = Pattern.compile( "<([^>]*?)(?=<|$)" );
    private static final Pattern P_XML_CONTENT = Pattern.compile( "(^|>)([^<]*?)(?=>)" );
    private static final Pattern P_STRAY_LEFT_ARROW = Pattern.compile( "<([^>]*?)(?=<|$)" );
    private static final Pattern P_STRAY_RIGHT_ARROW = Pattern.compile( "(^|>)([^<]*?)(?=>)" );
    private static final Pattern P_AMP = Pattern.compile( "&" );
    private static final Pattern P_QUOTE = Pattern.compile( "\"" );
    private static final Pattern P_LEFT_ARROW = Pattern.compile( "<" );
    private static final Pattern P_RIGHT_ARROW = Pattern.compile( ">" );
    private static final Pattern P_BOTH_ARROWS = Pattern.compile( "<>" );

    // @xxx could grow large... maybe use sesat's ReferenceMap
    private static final ConcurrentMap<String, Pattern> P_REMOVE_PAIR_BLANKS = new ConcurrentHashMap<>();
    private static final ConcurrentMap<String, Pattern> P_REMOVE_SELF_BLANKS = new ConcurrentHashMap<>();

    /**
     * set of allowed html elements, along with allowed attributes for each element
     **/
    private final Map<String, List<String>> vAllowed;
    /**
     * counts of open tags for each (allowable) html element
     **/
    private final Map<String, Integer> vTagCounts = new HashMap<>();

    /**
     * html elements which must always be self-closing (e.g. "<img />")
     **/
    private final String[] vSelfClosingTags;
    /**
     * html elements which must always have separate opening and closing tags (e.g. "<b></b>")
     **/
    private final String[] vNeedClosingTags;
    /**
     * set of disallowed html elements
     **/
    private final String[] vDisallowed;
    /**
     * attributes which should be checked for valid protocols
     **/
    private final String[] vProtocolAtts;
    /**
     * allowed protocols
     **/
    private final String[] vAllowedProtocols;
    /**
     * tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />")
     **/
    private final String[] vRemoveBlanks;
    /**
     * entities allowed within html markup
     **/
    private final String[] vAllowedEntities;
    /**
     * flag determining whether comments are allowed in input String.
     */
    private final boolean stripComment;
    private final boolean encodeQuotes;
    /**
     * flag determining whether to try to make tags when presented with "unbalanced" angle brackets (e.g. "<b text </b>"
     * becomes "<b> text </b>"). If set to false, unbalanced angle brackets will be html escaped.
     */
    private final boolean alwaysMakeTags;

    /**
     * Default constructor.
     */
    public HTMLFilter() {
        vAllowed = new HashMap<>();

        final ArrayList<String> a_atts = new ArrayList<>();
        a_atts.add( "href" );
        a_atts.add( "target" );
        vAllowed.put( "a", a_atts );

        final ArrayList<String> img_atts = new ArrayList<>();
        img_atts.add( "src" );
        img_atts.add( "width" );
        img_atts.add( "height" );
        img_atts.add( "alt" );
        vAllowed.put( "img", img_atts );

        final ArrayList<String> no_atts = new ArrayList<>();
        vAllowed.put( "b", no_atts );
        vAllowed.put( "strong", no_atts );
        vAllowed.put( "i", no_atts );
        vAllowed.put( "em", no_atts );

        vSelfClosingTags = new String[]{"img"};
        vNeedClosingTags = new String[]{"a", "b", "strong", "i", "em"};
        vDisallowed = new String[]{};
        vAllowedProtocols = new String[]{"http", "mailto", "https"}; // no ftp.
        vProtocolAtts = new String[]{"src", "href"};
        vRemoveBlanks = new String[]{"a", "b", "strong", "i", "em"};
        vAllowedEntities = new String[]{"amp", "gt", "lt", "quot"};
        stripComment = true;
        encodeQuotes = true;
        alwaysMakeTags = true;
    }

    /**
     * Map-parameter configurable constructor.
     *
     * @param conf map containing configuration. keys match field names.
     */
    @SuppressWarnings("unchecked")
    public HTMLFilter(final Map<String, Object> conf) {

        assert conf.containsKey( "vAllowed" ) : "configuration requires vAllowed";
        assert conf.containsKey( "vSelfClosingTags" ) : "configuration requires vSelfClosingTags";
        assert conf.containsKey( "vNeedClosingTags" ) : "configuration requires vNeedClosingTags";
        assert conf.containsKey( "vDisallowed" ) : "configuration requires vDisallowed";
        assert conf.containsKey( "vAllowedProtocols" ) : "configuration requires vAllowedProtocols";
        assert conf.containsKey( "vProtocolAtts" ) : "configuration requires vProtocolAtts";
        assert conf.containsKey( "vRemoveBlanks" ) : "configuration requires vRemoveBlanks";
        assert conf.containsKey( "vAllowedEntities" ) : "configuration requires vAllowedEntities";

        vAllowed = Collections.unmodifiableMap( (HashMap<String, List<String>>) conf.get( "vAllowed" ) );
        vSelfClosingTags = (String[]) conf.get( "vSelfClosingTags" );
        vNeedClosingTags = (String[]) conf.get( "vNeedClosingTags" );
        vDisallowed = (String[]) conf.get( "vDisallowed" );
        vAllowedProtocols = (String[]) conf.get( "vAllowedProtocols" );
        vProtocolAtts = (String[]) conf.get( "vProtocolAtts" );
        vRemoveBlanks = (String[]) conf.get( "vRemoveBlanks" );
        vAllowedEntities = (String[]) conf.get( "vAllowedEntities" );
        stripComment = conf.containsKey( "stripComment" ) ? (Boolean) conf.get( "stripComment" ) : true;
        encodeQuotes = conf.containsKey( "encodeQuotes" ) ? (Boolean) conf.get( "encodeQuotes" ) : true;
        alwaysMakeTags = conf.containsKey( "alwaysMakeTags" ) ? (Boolean) conf.get( "alwaysMakeTags" ) : true;
    }

    private void reset() {
        vTagCounts.clear();
    }

    // ---------------------------------------------------------------
    // my versions of some PHP library functions
    public static String chr(final int decimal) {
        return String.valueOf( (char) decimal );
    }

    public static String htmlSpecialChars(final String s) {
        String result = s;
        result = regexReplace( P_AMP, "&amp;", result );
        result = regexReplace( P_QUOTE, "&quot;", result );
        result = regexReplace( P_LEFT_ARROW, "&lt;", result );
        result = regexReplace( P_RIGHT_ARROW, "&gt;", result );
        return result;
    }

    // ---------------------------------------------------------------

    /**
     * given a user submitted input String, filter out any invalid or restricted html.
     *
     * @param input text (i.e. submitted by a user) than may contain html
     * @return "clean" version of input, with only valid, whitelisted html elements allowed
     */
    public String filter(final String input) {
        reset();
        String s = input;

        s = escapeComments( s );

        s = balanceHTML( s );

        s = checkTags( s );

        s = processRemoveBlanks( s );

        s = validateEntities( s );

        return s;
    }

    public boolean isAlwaysMakeTags() {
        return alwaysMakeTags;
    }

    public boolean isStripComments() {
        return stripComment;
    }

    private String escapeComments(final String s) {
        final Matcher m = P_COMMENTS.matcher( s );
        final StringBuffer buf = new StringBuffer();
        if (m.find()) {
            final String match = m.group( 1 ); // (.*?)
            m.appendReplacement( buf, Matcher.quoteReplacement( "<!--" + htmlSpecialChars( match ) + "-->" ) );
        }
        m.appendTail( buf );

        return buf.toString();
    }

    private String balanceHTML(String s) {
        if (alwaysMakeTags) {
            //
            // try and form html
            //
            s = regexReplace( P_END_ARROW, "", s );
            s = regexReplace( P_BODY_TO_END, "<$1>", s );
            s = regexReplace( P_XML_CONTENT, "$1<$2", s );

        } else {
            //
            // escape stray brackets
            //
            s = regexReplace( P_STRAY_LEFT_ARROW, "&lt;$1", s );
            s = regexReplace( P_STRAY_RIGHT_ARROW, "$1$2&gt;<", s );

            //
            // the last regexp causes '<>' entities to appear
            // (we need to do a lookahead assertion so that the last bracket can
            // be used in the next pass of the regexp)
            //
            s = regexReplace( P_BOTH_ARROWS, "", s );
        }

        return s;
    }

    private String checkTags(String s) {
        Matcher m = P_TAGS.matcher( s );

        final StringBuffer buf = new StringBuffer();
        while (m.find()) {
            String replaceStr = m.group( 1 );
            replaceStr = processTag( replaceStr );
            m.appendReplacement( buf, Matcher.quoteReplacement( replaceStr ) );
        }
        m.appendTail( buf );

        // these get tallied in processTag
        // (remember to reset before subsequent calls to filter method)
        final StringBuilder sBuilder = new StringBuilder( buf.toString() );
        for (String key : vTagCounts.keySet()) {
            for (int ii = 0; ii < vTagCounts.get( key ); ii++) {
                sBuilder.append( "</" ).append( key ).append( ">" );
            }
        }
        s = sBuilder.toString();

        return s;
    }

    private String processRemoveBlanks(final String s) {
        String result = s;
        for (String tag : vRemoveBlanks) {
            if (!P_REMOVE_PAIR_BLANKS.containsKey( tag )) {
                P_REMOVE_PAIR_BLANKS.putIfAbsent( tag, Pattern.compile( "<" + tag + "(\\s[^>]*)?></" + tag + ">" ) );
            }
            result = regexReplace( P_REMOVE_PAIR_BLANKS.get( tag ), "", result );
            if (!P_REMOVE_SELF_BLANKS.containsKey( tag )) {
                P_REMOVE_SELF_BLANKS.putIfAbsent( tag, Pattern.compile( "<" + tag + "(\\s[^>]*)?/>" ) );
            }
            result = regexReplace( P_REMOVE_SELF_BLANKS.get( tag ), "", result );
        }

        return result;
    }

    private static String regexReplace(final Pattern regex_pattern, final String replacement, final String s) {
        Matcher m = regex_pattern.matcher( s );
        return m.replaceAll( replacement );
    }

    private String processTag(final String s) {
        // ending tags
        Matcher m = P_END_TAG.matcher( s );
        if (m.find()) {
            final String name = m.group( 1 ).toLowerCase();
            if (allowed( name )) {
                if (false == inArray( name, vSelfClosingTags )) {
                    if (vTagCounts.containsKey( name )) {
                        vTagCounts.put( name, vTagCounts.get( name ) - 1 );
                        return "</" + name + ">";
                    }
                }
            }
        }

        // starting tags
        m = P_START_TAG.matcher( s );
        if (m.find()) {
            final String name = m.group( 1 ).toLowerCase();
            final String body = m.group( 2 );
            String ending = m.group( 3 );

            // debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending + "'" );
            if (allowed( name )) {
                final StringBuilder params = new StringBuilder();

                final Matcher m2 = P_QUOTED_ATTRIBUTES.matcher( body );
                final Matcher m3 = P_UNQUOTED_ATTRIBUTES.matcher( body );
                final List<String> paramNames = new ArrayList<>();
                final List<String> paramValues = new ArrayList<>();
                while (m2.find()) {
                    paramNames.add( m2.group( 1 ) ); // ([a-z0-9]+)
                    paramValues.add( m2.group( 3 ) ); // (.*?)
                }
                while (m3.find()) {
                    paramNames.add( m3.group( 1 ) ); // ([a-z0-9]+)
                    paramValues.add( m3.group( 3 ) ); // ([^\"\\s']+)
                }

                String paramName, paramValue;
                for (int ii = 0; ii < paramNames.size(); ii++) {
                    paramName = paramNames.get( ii ).toLowerCase();
                    paramValue = paramValues.get( ii );

                    // debug( "paramName='" + paramName + "'" );
                    // debug( "paramValue='" + paramValue + "'" );
                    // debug( "allowed? " + vAllowed.get( name ).contains( paramName ) );

                    if (allowedAttribute( name, paramName )) {
                        if (inArray( paramName, vProtocolAtts )) {
                            paramValue = processParamProtocol( paramValue );
                        }
                        params.append( ' ' ).append( paramName ).append( "=\"" ).append( paramValue ).append( "\"" );
                    }
                }

                if (inArray( name, vSelfClosingTags )) {
                    ending = " /";
                }

                if (inArray( name, vNeedClosingTags )) {
                    ending = "";
                }

                if (ending == null || ending.length() < 1) {
                    if (vTagCounts.containsKey( name )) {
                        vTagCounts.put( name, vTagCounts.get( name ) + 1 );
                    } else {
                        vTagCounts.put( name, 1 );
                    }
                } else {
                    ending = " /";
                }
                return "<" + name + params + ending + ">";
            } else {
                return "";
            }
        }

        // comments
        m = P_COMMENT.matcher( s );
        if (!stripComment && m.find()) {
            return "<" + m.group() + ">";
        }

        return "";
    }

    private String processParamProtocol(String s) {
        s = decodeEntities( s );
        final Matcher m = P_PROTOCOL.matcher( s );
        if (m.find()) {
            final String protocol = m.group( 1 );
            if (!inArray( protocol, vAllowedProtocols )) {
                // bad protocol, turn into local anchor link instead
                s = "#" + s.substring( protocol.length() + 1 );
                if (s.startsWith( "#//" )) {
                    s = "#" + s.substring( 3 );
                }
            }
        }

        return s;
    }

    private String decodeEntities(String s) {
        StringBuffer buf = new StringBuffer();

        Matcher m = P_ENTITY.matcher( s );
        while (m.find()) {
            final String match = m.group( 1 );
            final int decimal = Integer.decode( match ).intValue();
            m.appendReplacement( buf, Matcher.quoteReplacement( chr( decimal ) ) );
        }
        m.appendTail( buf );
        s = buf.toString();

        buf = new StringBuffer();
        m = P_ENTITY_UNICODE.matcher( s );
        while (m.find()) {
            final String match = m.group( 1 );
            final int decimal = Integer.valueOf( match, 16 ).intValue();
            m.appendReplacement( buf, Matcher.quoteReplacement( chr( decimal ) ) );
        }
        m.appendTail( buf );
        s = buf.toString();

        buf = new StringBuffer();
        m = P_ENCODE.matcher( s );
        while (m.find()) {
            final String match = m.group( 1 );
            final int decimal = Integer.valueOf( match, 16 ).intValue();
            m.appendReplacement( buf, Matcher.quoteReplacement( chr( decimal ) ) );
        }
        m.appendTail( buf );
        s = buf.toString();

        s = validateEntities( s );
        return s;
    }

    private String validateEntities(final String s) {
        StringBuffer buf = new StringBuffer();

        // validate entities throughout the string
        Matcher m = P_VALID_ENTITIES.matcher( s );
        while (m.find()) {
            final String one = m.group( 1 ); // ([^&;]*)
            final String two = m.group( 2 ); // (?=(;|&|$))
            m.appendReplacement( buf, Matcher.quoteReplacement( checkEntity( one, two ) ) );
        }
        m.appendTail( buf );

        return encodeQuotes( buf.toString() );
    }

    private String encodeQuotes(final String s) {
        if (encodeQuotes) {
            StringBuffer buf = new StringBuffer();
            Matcher m = P_VALID_QUOTES.matcher( s );
            while (m.find()) {
                final String one = m.group( 1 ); // (>|^)
                final String two = m.group( 2 ); // ([^<]+?)
                final String three = m.group( 3 ); // (<|$)
                // 不替换双引号为&quot;，防止json格式无效 regexReplace(P_QUOTE, "&quot;", two)
                m.appendReplacement( buf, Matcher.quoteReplacement( one + two + three ) );
            }
            m.appendTail( buf );
            return buf.toString();
        } else {
            return s;
        }
    }

    private String checkEntity(final String preamble, final String term) {

        return ";".equals( term ) && isValidEntity( preamble ) ? '&' + preamble : "&amp;" + preamble;
    }

    private boolean isValidEntity(final String entity) {
        return inArray( entity, vAllowedEntities );
    }

    private static boolean inArray(final String s, final String[] array) {
        for (String item : array) {
            if (item != null && item.equals( s )) {
                return true;
            }
        }
        return false;
    }

    private boolean allowed(final String name) {
        return (vAllowed.isEmpty() || vAllowed.containsKey( name )) && !inArray( name, vDisallowed );
    }

    private boolean allowedAttribute(final String name, final String paramName) {
        return allowed( name ) && (vAllowed.isEmpty() || vAllowed.get( name ).contains( paramName ));
    }
}